1. Field Of The Invention
The present invention relates generally to casing valves for use in the casing of a well, and more particularly, but not by way of limitation, to sliding sleeve cementing tools constructed for placement in a well casing.
2. Description Of The Prior Art
In the drilling of deep wells, it is often desirable to cement the casing in the well bore in separate stages, beginning at the bottom of the well and working upward.
This process is achieved by placing cementing tools, which are primarily valved ports, in the casing or between joints of casing at one or more locations in the well bore, flowing cement through the bottom of the casing, up the annulus to the lowest cementing tool, closing off the bottom, opening the cementing tool, and then flowing cement through the cementing tool up the annulus to the next upper stage and repeating this process until all stages of the well are cemented.
Cementing tools used for multi-stage cementing usually have two internal sleeves, both of which are usually shear-pinned initially in an upper position, closing the cementing ports in the tool. To open the cementing ports a plug is flowed down the casing and seated on the lower sleeve. Fluid pressure is then increased in the casing until sufficient force is developed on the plug and sleeve to shear the shear pins and move the lower sleeve to the position uncovering the cementing ports. Cement is then flowed down the casing and out the ports into the annulus. When the predetermined desired amount of cement has been flowed into the annulus another plug is placed in the casing behind the cement and flowed down the casing to seat on the upper sleeve. The pressure is increased on the second plug until the shear pins holding it are severed and the upper sleeve is moved down to close the cementing ports.
One cementing tool of the type just described is disclosed in U.S. Pat. No. 3,768,556 to Baker, assigned to the assignee of the present invention.
One improvement upon the Baker '556 device is found in U.S. Pat. No. 4,246,968 to Jessup et al., and also assigned to the assignee of the present invention. The '968 patent discloses a device similar to that of the Baker '556 patent, except it has added a protective sleeve which covers some of the internal areas of the tool which are otherwise exposed when the internal sleeves move downward to close the port. This protective sleeve prevents other tools which may later be run through the cementing tool, from hanging up on the inner bore of the cementing tool.
Another approach which has been utilized for cementing tools is to locate the closure sleeve outside the housing of the tool. A line of tools distributed by the Bakerline Division of Baker Oil Tools, Inc., known as the Bakerline Model "J" and Model "G" stage cementing collars have closure sleeves located outside the housing of the tool. These closure sleeves have a differential area defined thereon and are hydraulically actuated in response to internal casing pressure which is communicated with the sleeves by movement of an internal operating sleeve to uncover a fluid pressure communication port. The Bakerline devices are disclosed in the 1982-1983 Product Service Catalog of the Bakerline Division of Baker Oil Tools, Inc., which catalog is entitled "Stage and Stab-In Cementing Equipment and Services BL-482", at page 4 thereof.
Also, the prior art includes non-rotating cementing plug sets as seen in U.S. Pat. No. 4,858,687 to Watson et al.
There is a need for a stage cementing tool which is relatively compact and simple of design, and yet provides reliable operation and a smooth, unobstructed bore after completion of the cementing job.